The European Aviation Safety Agency (EASA) issued an emergency AD for specific Rolls-Royce Trent 1000 engines, as a result of an incident in November 2016.

A Scoot Boeing 787-9 Dreamliner returned to land at Singapore Airport after the crew performed an engine in-flight shut-down (IFSD) following N2 vibration and multiple messages.
The post-flight borescope inspection of the engine revealed an intermediate pressure turbine blade (IPTB) missing at the shank. Analysis shows that this kind of failure was due to sulphidation corrosion cracking.
Initial actions included and AD (2017-0056) that required removal from service of certain engines. Since that AD was issued, prompted by further occurrences and analyses, it has been decided that, to reduce the risk of dual IFSD, a new cyclic life limit must be applied to certain engines, which determines when an engine can no longer be installed on an aeroplane in combination with certain other engines.
For this reason, the EAD requires de-pairing of the affected engines. This AD is considered an interim action and further AD action may follow.